1. Field of the Invention
The present invention relates to a thermoplastic multilayer sheet for packaging granular bulk materials such as dry pet food, and in particular, a thermoplastic multilayer ethylene polymer sheet which is recyclable and when formed into a packaging construction such as a bag prevents the emanation of odoriferous components of the packaged product from escaping into the atmosphere.
2. The Prior Art
Dry pet food is typically sold, for reasons of economy and convenience, in bulk quantities. Pet food which contains animal fat and protein ingredients emits an odor when stored. The pet food, in the form of pellets, is normally packaged in plastic-lined paper bags or wax-lined paper bags which are effective to prevent the emission of odor during the time the pet food product is shipped and stored.
A problem with the packaging normally used for pet food is the material of construction. As pet food bags for example are generally multi-substrate systems combining paper or wax-paper and plastic, the disposal of such multi-substrate packaging is uneconomic and injurious to the environment. Packaging constructed of multilayer like substrate materials would allow recycling of the packaging with the attendant environmental and economic advantages thereof.
Thermoplastic sheet, and in particular polyolefin sheet materials, have been used for some time in connection with packaging of various articles including food products which require resistance to abuse and stress, an attractive shelf appearance, and protection from the environment during the distribution cycle. When it is normally attempted to manufacture pet food bags using a single substrate multilayer system such as polyolefin laminate sheet which would be recyclable, it is found that when pet food products are packaged in such bags, and particularly high grain content pet food coated with grease for paintability, the packaged pet food product when stored in an enclosed area for a limited period of time, e.g., a day or less, emanates a disagreeable odor, which odor is offensive to anyone entering the area. Bags manufactured from a multilayer sheet of low density polyethylene, linear low density polyethylene or a combination of these polymeric materials in addition to poor odor retention, exhibit poor stiffness properties, This latter defect results in poor shelf presence when the packaged pet food product is made available for sale in retail stores resulting in limited acceptance of the packaged product by pet owners.
There is therefore a need in the art for a recyclable plastic bag used for the packaging of odoriferous materials which not only has suitable odor retention characteristics, but one which also has consumer acceptability with respect to its appearance.